Sadly, our Early Bronco project has been languishing. That's for a few reasons, and not all are worth going into during this tale of Bronco construction. The main reason for this rig resting idle is because of our personal indecision as it comes to what transmission to run in the Bronco. Generally we are all for manual transmissions, but we also enjoy a good automatic every now and again.
The Bronco came to us with no transmission, but in its former life it had an NV4500, and before that an NP435. Despite this, for whatever reason we've decided this particular iteration of this vehicle needs an automatic. And sometimes making a solid decision eludes us. We've contemplated everything from the venerable and original Ford C4 and beyond for this project. We eventually shied away from the C-4 because of the Bronco's relatively deep 4.88:1 axle gears. Those combined with a healthy BluePrint 306ci Bronco Edition small-block engine would make for fun, albeit quick runs up to about a maximum of 55 mph. We'd like to occasionally drive faster than that, so the idea of a C4 was dropped in favor of an auto with an overdrive.
So it has been a while, but the BluePrint Bronco Edition 306ci V-8 has been safely stowed in its crate and accompanying plastic bag. We opened it up and pulled off the Holley Sniper EFI and bolted on our engine lift plate. With that done, we hoisted the engine up in the air and loosened the bolts holding the crate to the engine. Then installed two new motor mounts from our local parts store.
Enter Ford's AODs, AODEs, and 4R70W (these are the evolution of Ford small-block automatic overdrive transmissions), and more recently we've also learned more about Ford factory offerings with multiple speeds.
So with lots of information on what is possible to bolt between our small-block BluePrint engine and our freshly rebuilt Ford Dana 20 we've finally made a decision and have a fresh Ford 6R80 transmission from Performance Automatic in hand. The reasons are many. The Ford 6R80 is a beefy unit, rated to 590 lb-ft of input torque as it is one of the transmissions designed to live behind healthy V-8s in Ford's more modern SUVs and trucks. That also means it has some beneficial ratios for our usage. First gear is a deep 4.17:1, and the transmission has not one, but (count 'em!) two overdrives, the first at 0.87:1 and the second at a tall 0.69:1. Couple that with our T-shift Ford Dana 20's 2.46:1 low range and it should make for good crawling off-road as well as keep the 4.88:1 axle gears spinning fast on the highway while in two-wheel drive.
Adapters are a yes front and rear with this transmission because it never came with an early Bronco Dana 20, nor was it ever found behind a small-block Windsor Ford V-8. Lucky for us, Advance Adapters has a 6R80-to-Early Bronco Dana 20 adapter and a crossmember (the company is working on a shifter for this combo), and Performance Automatic makes adapters to fit a small-block Windsor V-8 to a transmission and torque converter designed to bolt to a late-model modular Ford V-8 engine.
Add in an electronic transmission controller, and with any luck the BluePrint Bronco Edition 306ci V-8 will haul our Bronco down the road and trail—once we get to wiring the rig, that is. For now, here's the mechanical action of bolting in an engine, adding a transmission, and bolting on at T-case.
With the Bronco on our BendPak 10K lift we pulled the tires and dropped the body and chassis down as low as possible to heft the engine up and over the grille. Hindsight being what it is, we probably should have pulled the grille, core support, and front fenders to install the engine. Still, with the Bronco basically sitting on its axles the install of the engine was easy.
Here are all the goodies. Well, most of them anyway. Shown are the Ford 6R80 transmission from Performance Automatic, the Ford Dana 20 T-case to 6R80 transmission adapter from Advance Adapters, Advance Adapter's new 6R80-to-Early Bronco crossmember and transmission mount, and more. The boxes from Performance Automatic hold the 6R80-to-Windsor small-block adapters and torque converter adapter bolts, and the wiring harness and computer controller for the six-speed auto.
To the left are the Performance Automatic Modular V-8 6R80 to Windsor engine adapter plates and hardware. The adapter plates don't look like much, but they allow the back of the engine to fit this newfangled transmission. To the right are the torque converter bolt spacers and an aluminum torque converter indexing ring (which we ended up not needing).
The studs welded to the 6R80's rebuilt torque converter have to be trimmed down slightly so the spacers can be installed flush against the body of the torque converter. To trim them down, we first installed an M10x1.0 nut to save the threads and also set the depth of material we would be removing. Our implement of destruction for this task is a 4 1/2-inch angle grinder with an abrasive flap wheel.
With the torque converter bolt spacers installed we mocked up one of the adapter plates to the 6R80 transmission so we could clearance part of the factory bellhousing for the Bronco's small-block starter. We then used a reciprocating saw and a cutoff wheel to trim the material from inside the starter C for the new, uh, old starter.
It's kind of hard to trim away part of a perfectly good and freshly rebuilt transmission because once the first cut is made there's little going back. We love the sound of a Windsor engine, and while a Modular V-8 would bolt to this transmission without modifications, we like the idea of the old-school engine in front of this modern transmission. With the material removed from the bell we checked fitment with the starter, trimming as necessary.
Next we installed a flex plate intended for a 1988 F-150 with a 164-tooth starter gear and a 50-ounce external balance as called for by BluePrint Engines. Not shown, but essential to mating this flex plate to the 6R80's torque converter with the previously shown spacers, was opening the four torque converter bolt holes outward about 1/8 inch per side. We secured the flex plate with fresh, fine-threaded 7/16x1-inch Grade 8 bolts and red thread-locking compound. Also shown are the Performance Automatic adapter plates and some of the hardware. At the end of the day, six bolts hold the adapter plates and transmission directly to the engine block.
We then used a rickety old transmission jack and the BendPak 10K lift to position the Bronco and install the transmission behind the 306ci V-8. This is when we found out the hard way that the aluminum torque converter spacer wasn't necessary for this application and that the bolt holes in the flex plate had to be opened up. We then installed the front half of the Advance Adapters 6R80 to Ford Dana 20 transfer case adapter using some new M10x1.25 bolts. Don't forget the one bolt in the 6 o'clock position.
Here's the Dana 20 transfer case with the other two aluminum parts of the Advance Adapters adapter kit with a captured bearing, a spud shaft, and hardware. The Ford Dana 20 input gear goes on the spud shaft, which is then retained in the transfer case with the bearing and the smaller aluminum ring. The larger aluminum ring gets a gasket and holds everything in place inside the transfer case.
The outer ring has a clocking mark that has to be roughly at the 10 o'clock position for all the bolt holes to line up. Like all Advance Adapter kits, the Ford Dana 20 to Ford 6R80 adapter kit has all the bolts, washers, indexing dowels, and gaskets you'll need to bolt the parts together.
With the transmission held in place with the Advance Adapters 6R80-to-Early Bronco crossmember, we deadlifted the Dana 20 with adapters in place and secured it with the included fasteners. It's a good idea to have a friend nearby for this because while the Dana 20 with adapters isn't the heaviest transfer case, it is awkward to hold in place while starting the bolts. The Advance Adapters adapter ring also allows for at least three clocking positions for the Dana 20 to ride at. Since we have long-arm suspension with brackets hanging down, we don't mind rotating the case down for the best front driveline angle.
With the mechanical parts of the drivetrain in place we'll call it a day for now, but we will have to install the 6R80's controller and wiring harness and integrate it into the Holley Sniper EFI wiring harness so the two can play nice. That job will have to wait for the next installment of our slow Early Bronco build.
Paso Robles, CA